Sunday 4 December 2011 10.00 EST
First published on Sunday 4 December 2011 10.00 EST

The political importance of transport in London has been firmly underlined in the past couple of weeks, with the two frontrunners for next year's mayoral election vying for advantage like irate motorists at a red light. A new opinion poll has placed Conservative incumbent Boris Johnson in the electoral driving seat with an eight-point lead. But respondents also made clear their wish for lower public transport fares, a treat that Labour's Ken Livingstone has been promising.

The Labour camp is taking heart. The celebrity Tory's multitude of media cheerleaders and chums are gently warning him to get his finger out. Expect his response to combine protestations of financial responsibility with a diversion of our attention towards Christmas period novelties such as the introduction of the first of his (pretty good) new-style London buses and the completion of his (pretty pointless) removal of the "bendy" variety – two conspicuous incarnations of what a London Labour MP, not a fan of Livingstone, describes as Johnson's "cakes and ale" mayoralty.

George Osborne, whose boss will do all he can afford to keep Johnson in City Hall – and therefore out of his hair in the House of Commons for as long as possible – has tried to help. His autumn statement's cap on national rail fare increases means that the 7% hike across the public transport tariff board that was heading Londoners' way in January will be reduced to 5.6%. Vague and qualified support for new ways for cars to cross the Thames have enabled Johnson to generate headlines suggesting that a great string of brilliant bridges and terrific tunnels are practically half-built already.

The task for his "underdog" challenger is to drag working Londoners' attention back to transport basics, especially their relationship to spending power. I hope it works: Livingstone's vision for transport was far more coherent than Johnson's in 2008, and the latter's priorities in office have been regressive policies and self-promotion. But the wider truth confronting all candidates for mayor is that they're short of room for bolder manoeuvres.

That's the squeezed economy for you, stupid. Livingstone said in a recent speech that under Johnson Transport for London (TfL) has hoarded a crock of cash big enough to maintain an investment programme as well as sustain his fare deal pledge, but every pound less he'd take in fares would be a pound less for him to spend. He's already ruled out reversing Johnson's halving of the congestion charge zone, blaming set-up costs, even though the Tory's vote-seeking decision has deprived TfL of at least £50m a year in income. He's talked of trams and of reviving other schemes that Johnson has canned, but how persuasive will he be given any mayor's dependence on the Treasury and voters' reluctance to trust him?

The Conservative alternative looks set to be just more of the same: steadfast defence of motorists' privileges; high-profile half-measures for cyclists; media-pleasing lobbying for an estuary airport in Kent that London mayors have no authority to build. Meanwhile, bus usership is rising – it often does when money's tight because it's cheaper than driving or the tube – with capacity, as the London assembly's assiduous Liberal Democrats as well as Labour keep pointing out, failing to keep pace. And, of course, those fares will keep on rising too.

London transport's ideal direction of travel would be much greener, much cleaner, towards cheaper public transport and far more in favour of pedal and pedestrian power. More road-pricing not less would literally help clear the way, enabling the capital's economy to flow more efficiently and its top tier of government to raise a lot of money too: a market remedy for social and economic ills that's been backed by free-enterprise thinkers from Milton Friedman to Edward Glaeser. Yet the Lib Dems' proposal for a clean air zone is about the only potentially transformative idea knocking around. It's early days in the election campaign, but these are pragmatic times. London mayors have more control over transport than anything else, but the austerity age highlights yet again how limited even those controls are.